My leaflets went out with 4 or 5 others...always. It didn't bother me, as I still got 4 custys per thousand and at £30 plus VAT, (delivery cost only), to areas of my choice, I couldn't complain. Also, the company that delivered them made sure they had the full 5 leaflets to deliver, so the date they were due to go out often changed. There was usually a hold up with another leaflet. Having said that, they were all delivered and I did ok out of it.
If you're not sure, try doing 5k and see how it goes. Unfortunately, with advertising, the only way to see what works best for YOU, in YOUR area is to 'test the water'.
Good luck.